Butadiene rubbery copolymer stabilized with 2, 4-dimethyl-6-octylphenol



Patented July 29, 1952 BUTADIENE RUBBERY COPOLYMER STA- BILIZED WITH PHENOL 2,4-DIMETHYL-6-OCTYL- Leland J. Kitchenand George E. P. Smith, Jr., Akron, Ohio, assignors to The Firestone Tire & Rubber Company, Akron, Ohio, a corporation of Ohio .9 No Drawing. Original application March 9, 1946,

Serial No. 653,425.

Divided and this application May 10, 1951, Serial No. 231,449

This invention relates to stabilizers of rubberlike "copolymers of a conjugated diene-such as, for example, butadiene, isoprene, Z-cyanobutadiene, pentadiene, piperylene, dimethylbutadiene, etc.and a nitrile of the general formula CH2=C(R) CN Where R is H, CH3, 021-15, 03H? or C1. The stabilizers preserve both the uncured and cured copolymers from stiffening and from atmospheric deterioration. The invention includes compositions which contain the stabilizer and methods of using the stabilizer. It will be described more particularly as applied to the stabilization of rubber-like copolymers of butarecognized as antioxidants for these rubber-like materials. These secondary aryl amines, when used alone, are eiiective stabilizers but discolor badly and are not satisfactory for use in lightcolored stocks, such as those weighted with zinc oxide, titanium dioxide or the like and .used in the whiteside walls of tires, for example.

The stabilizers of this invention are the 2,4-dimethyl-6-octylphenols. The octyl group is preferably a tertiary octyl radical. A preferred stabilizer, 2,4-dimethyl-6-(alpha,alpha,gamma, gamma-tetramethylbutyl) phenol, may be prepared by alkylating ZA-dimethylphenol by means of diisobutylene, for example as described in detail below.

While the stabilizers of this invention may be added to the copolymer composition to be preserved in any conventional manner, such as by mill or Banbury mixing, they are preferably added directly to the latex which results from the emulsion copolymerization. Thus, the stabilizer is incorporated before coagulation and drying of the copolymer have been effected. It is of advantage to add the stabilizer to the latex as soon as possible after the copolymerization reaction has been carried out to the degree desired because of the comparative instability of unstabilized copolymer, both in the latex form and in the coagulated form.

The stabilizers'of this invention are not to be confused with the so-called stabilizers which impart coagulation resistance to the latex. The stabilizers of this invention impart to the rubber- Claims. (0 1. 260-4595) like copolymer a resistance to aging evidenced by resistance to deteriorative changes, such, as stiffening, set-up, loss of tensile strength, discoloration or embrittlement, which tend to, take place when such rubber-like materials in which no stabilizer is incorporated are aged or treated at elevated temperatures, and for particularly unstable copolymers, even at room temperatures. Such deteriorative changes are thought to be associated, in part, with oxygen.

The stabilizers of this invention are of the nondiscoloring type. They have special value when used with white or light-colored copolymer compounds. In the production of the copolymers for such use, the stopping agents employed should be of the nondiscoloring type. Hydroquinone, frequently used as a stopping agent, tends to discolor latices to which itis added and its use should be avoided. i.

If it is not convenient to use a nondiscoloring stopping agent in preparing the copolymer-to be used in carrying out this invention, the use of a stopping agent maybe dispensed with, particularly if'the copolymer is coagulated and dried within several hours after the desired degreeoi copolymerization has been reached. The latices used in the following examples were prepared without any stopping agent to obtain clear-cut stabilizer tests and avoid the possibility of obscuring test results by the transient stabilizer action which sometimes accompanies theuse of certain stopping agents.

The stabilizer is conveniently addedto the latex in emulsion form. For example, it maybe emulsified in 5 per cent sodium oleate solution. A stabilizer which is solid at room temperature may be emulsified by first dissolving it in a small volumeof warm alcohol and then adding. the alcohol solution to about four times its volume of stirred aqueous sodium oleate solution.

After coagulation of the latex, the commercial drying of the copolymer is carried out at an elevated temperature; e. g., 240 F. for a period of 50 to minutes. These conditions are sufiicienty drastic to cause discoloration. and stiifening of unstabilized copolymer, especially-those copolymers which are not high in acrylonitrile content; e. g., those with an a'crylonitrile content of 30 per cent or less. Consequently, to'produce the best light-colored copolymer, the stabilizer should be present during the drying operation.

Unstabilized copolymer deteriorates: on standing. For instance-storage for one yearv at 25-? C. is approximately equivalentto four-daysi. oven: aging of the copolymer at C. The copolymer 3 to which stabilizer is added in latex form is capable of storage, even at higher temperatures, withoutv substantial deterioration..

.On thelaboratory scale, wet copolymer samples were dried 20 hours at IO-75 0., this drying being less conducive to discoloration and other effects of aging than the higher temperature methods used commercially. The followingtable '4 Effectiveness of the alkylated phenol as a stabilizer for the copolymer was demonstrated by oven-aging samples of thetest copolymer and the control for 96 hours at 100 C. At the end of this aging period, both test and control were in good condition and both were set-up or heatcured to a similar degree. The degree of heatcuring of the two copolymer samples then was gives the results of this test which are typical" of results produced by the use of the stabilizer of this invention: 7

Color Condition Stabilized copolymer White Nonlieatcured. Unstabillzed copolymer Cream tolight tan flfiitgureg and ene 1 Heatcured means evidence of incipient deteriorationresembling a slight degree of vulcanization.

The noted change inthe physicalv properties of the unstabilized copolymer is undesirable. because it renders it more difli'cult to process. and

"necessitates reversal" by mill breakdown which is time consuming andfexpensive.

' 2,4i-dimeth1/Z-6-(alphanlphagammaganimatetmmcthylbutyl) phenol Fifty" grams of 2;l-dimethylphenol containing 'figrams of catalyst (45. per cent boron trifiuoride in ether) were stirred while-adding'200 grams of dii'sobutylene by means of. a' dropping funnel during a period. of 15 minutes The temperature rose to-60 C.; and stirring was continued at 50- 50 1mm; plate) for an hour after the addition of diisobutylene was complete. The reaction mix:-

tuife 'was washed with water and then dilute sodium: hydroxidesolution, dried over anhyd. potassium carbonate, and. distilled through'a 1- foot columnpacked with Raschig rings to yield d8fgrams (71 per cent) of 2,4-dimethyl'-6'-(alpha,-

alpha,ga'mmagamma-tetramethylbutyl) phenol, a water-white, slightly viscous'liquid with practically no odor and having B; P; 144-1455" at 10 'mm. and refractive index, 12 15106. trialkyl phenol was. found to bean efiecti-v'e stabilizer for butadiene-acrylonitrile copolymer when tested in copolymer of the typ'ehigh in acrylonitrile content, being not only of the same order of eifectiveness as phenyl beta-naphthylamine but also yielding a stabilized copolymer nondiscoloring in nature when incorporated in the otherwise uninhibited Copolymer in place of the customary discoloring antioxidant. For comparative purposes, copolymer samples were prepared 'from the same uninhibited latex by addition of sodium'oleate solution containing no stabilizer in emulsion to serve as blanks. Controls were prepared by adding an emulsion of zper cent phenyl beta-naphthylamine (a standard efiective stabilizer for use in butadiene-acrylonitrilecopolymer compositions) in sodium oleate'solution prepared in like manner. The test sample was prepared in a'similar mannerby adding'an'emulsion of 2 per cent of the trialkyl phenol in sodium oleate solution to the uninhibitedlatex.

ascert'ained'by'a milling procedure. A l80-gram sample of copolymer which had been aged as described above (96 hours at 100 C.) was folded V twice and passed. through a cold mill (circulating water) once; The rolls of the mill were set at a distance of 0.05 inch apart. The sample was then milled; and the time required for a band without holes to. form, on the outer roll of the mill was noted. The testscompared as follows:

Break-down Time after Aging 96 Hours at Seconds Test Control Color after 0010; after Drying and before Aging f Test white tan; Control brown brown.

The alkylated phenol is satisfactory for drying without discoloration.

Effectiveness of this trialkyl phenol as stabilizer for vulcanizates based upon butadiene-acrylonitrile copolymer compositions was determined by mixing the above copolymer samples according to Formula 1:

FORMULA 1 7 Parts Copolymer (with and without stabilizer) 100.0

Stearic acid 3.5 Sulfur 2.0 Zinc oxide 5.0 Carbon black 40.0 Accelerator (cyclohexyl benzothiazyl sulfenamide) 1.3

vulcanization conditions were minutes of cure at 274 F. The following physical testing data was obtained:

' NORMAL PROPERTIES I.

. Test I 3009' Elon- Vulcamzate from. Copolymer Modulus Tensile gation Unaged copolymer.... 1, 4, 200 600 Do 1,000 4, 325 6 10 Oven-aged copolymer 1, 325 4, 1-75 590 4 days at ll0 O Controll, 275 3, 675 540 In evaluating the data on aging of vulcanizate compositions derived from synthetic copolymers of this type, both modulus and tensile changes should be considered. Loss of vulcanizate quality results both in lowering of tensile strength and increase in modulus. The marked changes in modulus in the above tests demonstrates the equivalence in stability of the test stock to the control stock.

The test antioxidant and stabilizer was found to impart no discoloration to white test vulcanizates. Test stocks were mixed according to the following formula:

FORMULA 2 Parts Polymer containing 2% stabilizer 100.0 Coumarone resin 7.5 Sulfur 2.25 Magnesium oxide 5.0 Zinc oxide 85.0 Neutral clay 20.0 Titanium dioxide 20.0 Benzothiazyl disulfide 1.1 Zinc diethyldithiocarbamate 0.2

The vulcanizates (cured 40 minutes at 280 F.) had the following colorations after exposure tests Fadeometer Test Sunlamp Exposure, Hours at 125 1. 16 Hours at 7 Inches st white white. Control brown brown.

Thus, the stabilizers of this invention prevent stiffening of the uncured copolymer during drying without substantial discoloration, and prevent stifiening of the uncured copolymer during milling, and this, too, without substantial discoloration. Also, they serve as antioxidants in the vulcanizate and without substantial discoloration. They are, therefore, particularly useful in white and other light-colored compositions although they may also be added to dark products. Although the specific example of the invention discloses, stabilization of the copolymer by means of 2 per cent of the stabilizer, larger or smaller proportions of the stabilizer may be employed as is known in the art of synthetic rubber compounding. Ordinarily, less than 5 parts of stabilizer per parts of copolymer will be used. This application is a division of application Serial No. 653,425, filedMarch 9, 1946, now abandoned.

What we claim is:

1. Uncured, rubber-like copolymer of butadiene and acrylonitrile stabilized with 2,4-dimethyl-6- (alpha,alpha,gamma,gamma tetramethylbutyl) phenol.

2. Cured, rubber-like copolymer of butadiene and acrylonitrile stabilized with 2,4-dimethyl-6- (alpha,alpha,gamma,gamma tetramethylbutyl) phenol.

3. The process of drying uncured, rubber-like copolymer crumb from the emulsion copolymerization of butadiene and acrylonitrile, which comprises drying the same in the presence of 2,4- dimethyl 6-(alpha,alpha,gamma,gamma-tetramethylbutyl) phenol.

4. Rubber-like copolymer of butadiene and acrylonitrile stabilized with 2,4 dimethyl 6- octylphenol.

5. Rubber-like copolymer of butadiene and acrylonitrile stabilized with 2,4-dimethyl-6-tertoctylphenol.

LELAND J. KITCHEN. GEORGE E. P. SMITH, JR.

No references cited. 

4. RUBBER-LIKE COPOLYMER OF BUTADIENE AND ACRYLONITRILE STABILIZED WITH 2,4 - DIMETHYL-6OCTYPHENOL. 